Geoscience Reference
In-Depth Information
Sedimentary and biogenic
structures
Clay and quartz
content
Lithofacies
Texture
Colour
Hardness
Bedding
Reservoir quality
Laminated
chalk facies
Carbonate mudstones
composed of calcareous
mud generally devoid
of framework material,
except for sporadic
occurrences of rare,
macroscopic skeletal
material.
Light grey to
yellowish brown
in colour.
Well indurated, and
hard, although
hardness is variable.
Medium bedded
with bedding
commonly
defined by the
presence/absence
of laminations.
Common, thin, planar-
parallel laminations.
< 2% quartz
in the Tor
Formation; 1%
to 20% quartz
in the Ekofisk
Formation. < 1%
clay minerals.
Laminated chalk
seldom exhibit
reservoir
quality
porosity.
Burrowed
Laminated
chalk facies
Carbonate mudstones
composed of
calcareous mud and
generally devoid of
framework material.
Light grey to
yellowish
brown.
Well indurated, and
hard, although
hardness is somewhat
variable.
Bedding, which is
most commonly
defined by
variability in
the degree of
burrowing, ranges
from thin (<10
centimetre) to very
thick (>1 metre).
Planar to somewhat wavy
parallel laminations
disrupted by rare to
common
Planolites
and
Chondrites
burrows.
10% to 35% quartz
in the Magne
and Ekofisk
Formation, < 2%
quartz in the Tor
Formation.
Burrowed
Laminated
chalk intervals
contain
occasional,
poor reservoir
quality
porosity.
Homogeneous
chalk facies
Calcareous mudstones
containing little or no
framework material.
Yellowish
brown to dark
yellowish brown
or very rarely
light grey.
Well indurated, and
very commonly
soft to occasionally
somewhat hard.
Primary bedding
is absent, or at
best, difficult to
recognise.
Uniform, massive lacking
of any internal structure,
although occasionally,
very rare burrows may
occur in some thinner
units.
1% to 4% quartz
and 1% to 2%
clay minerals are
common in the
Tor Formation;
2% to 15%
quartz and 1% to
5% clay minerals
are more
representative
of the Ekofisk
Formation.
Commonly
contains very
good reservoir
porosity;
commonly the
best reservoir
porosities
that occur
in a well are
associated with
homogeneous
chalk.
1% to 3% quartz,
< 2% clay
minerals.
Burrowed
Homogeneous
chalk exhibit
occasional
reservoir
quality
porosity.
Burrowed
Homogeneous
chalk facies
Calcareous mudstones
that contain little,
if any, framework
material.
Yellowish brown
to light grey in
colour.
Well-indurated, and
hard to moderately
soft.
If primary bedding
can be recognised,
it occurs in the
medium to thick
range (>1 metre).
Fairly uniform and
massive chalks, but
contain very rare to
rare (to occasionally
common),
Chondrites
and
Planolites
and
burrow mottling.
Pebble
floatstone
facies
Calcareous mudstones
to wackestones, and
very rarely packstones,
that contain rare to
locally abundant,
high-sphericity, round,
sand-sized to pebble-
sized chalk clasts.
Yellowish brown
to light grey in
colour.
Well indurated, and soft
to hard.
Primary bedding,
when recognised,
ranges from
medium to thick
(>1 metre) defined
by clast content
and texture.
Pebble Floatstones are
either massive or exhibit
normal graded bedding.
1% to 3% quartz,
< 1% clay
minerals.
Pebble floatstones
exhibit
reservoir
quality
porosity.
Search WWH ::
Custom Search